The statement EXPLAIN running as regular statement and as prepared statement produces different results for UPDATE with subquery

MariaDB [test]> CREATE TABLE t1 (c1 INT KEY) ENGINE=MyISAM;

Query OK, 0 rows affected (0,128 sec)

MariaDB [test]> CREATE TABLE t2 (c2 INT) ENGINE=MyISAM;

Query OK, 0 rows affected (0,023 sec)

MariaDB [test]> CREATE TABLE t3 (c3 INT) ENGINE=MyISAM;

Query OK, 0 rows affected (0,021 sec)

MariaDB [test]> EXPLAIN EXTENDED UPDATE t3 SET c3 = ( SELECT COUNT(d1.c1) FROM ( SELECT a11.c1 FROM t1 AS a11 STRAIGHT_JOIN t2 AS a21 ON a21.c2 = a11.c1 JOIN t1 AS a12 ON a12.c1 = a11.c1 ) d1 );

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-----------------------------------------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                               |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-----------------------------------------------------+

|    1 | PRIMARY     | t3    | ALL  | NULL          | NULL | NULL    | NULL |    0 |   100.00 |                                                     |

|    2 | SUBQUERY    | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | Impossible WHERE noticed after reading const tables |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+-----------------------------------------------------+

2 rows in set (0,002 sec)

MariaDB [test]> PREPARE stmt FROM "EXPLAIN EXTENDED UPDATE t3 SET c3 = ( SELECT COUNT(d1.c1) FROM ( SELECT a11.c1 FROM t1 AS a11 STRAIGHT_JOIN t2 AS a21 ON a21.c2 = a11.c1 JOIN t1 AS a12 ON a12.c1 = a11.c1 ) d1 )";

Query OK, 0 rows affected (0,000 sec)

Statement prepared

MariaDB [test]>  EXECUTE stmt;

+------+-------------+-------+------+---------------+------+---------+------+------+----------+--------------------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                          |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+--------------------------------+

|    1 | PRIMARY     | t3    | ALL  | NULL          | NULL | NULL    | NULL |    0 |   100.00 |                                |

|    2 | SUBQUERY    | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | no matching row in const table |

+------+-------------+-------+------+---------------+------+---------+------+------+----------+--------------------------------+

2 rows in set (0,000 sec)

MariaDB [test]> PREPARE stmt FROM "EXPLAIN DELETE FROM t3 WHERE c3 = ( SELECT COUNT(d1.c1) FROM ( SELECT a11.c1 FROM t1 AS a11 STRAIGHT_JOIN t2 AS a21 ON a21.c2 = a11.c1 JOIN t1 AS a12 ON a12.c1 = a11.c1 ) d1 )";

Query OK, 0 rows affected (0,001 sec)

Statement prepared

MariaDB [test]> EXECUTE stmt;

+------+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                          |

+------+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+

|    1 | PRIMARY     | t3    | ALL  | NULL          | NULL | NULL    | NULL |    1 | Using where                    |

|    2 | SUBQUERY    | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL | no matching row in const table |

+------+-------------+-------+------+---------------+------+---------+------+------+--------------------------------+

2 rows in set (0,001 sec)

MariaDB [test]> EXPLAIN DELETE FROM t3 WHERE c3 = ( SELECT COUNT(d1.c1) FROM ( SELECT a11.c1 FROM t1 AS a11 STRAIGHT_JOIN t2 AS a21 ON a21.c2 = a11.c1 JOIN t1 AS a12 ON a12.c1 = a11.c1 ) d1 );

+------+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra                                               |

+------+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+

|    1 | PRIMARY     | t3    | ALL  | NULL          | NULL | NULL    | NULL |    1 | Using where                                         |

|    2 | SUBQUERY    | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL | Impossible WHERE noticed after reading const tables |

+------+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+

2 rows in set (0,001 sec)